<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        var num=0;
        function sum(a) {
            num++;
            if (num == 3) {
                
            }
            return sum
        };

        sum(1)(2)(3)
        console.log(111);
    </script>
</body>

</html>